1. Field of the Invention
This invention relates to a liquid jet recording head which jets liquid and forms flying liquid droplets for recording.
2. Description of the Prior Art
Ink jet recording methods such as jet recording, have recently drawn attention in that noise occurring during recording is negligible high-speed recording is possible and recording can be accomplished without requiring a special process to fix images on so-called plain paper.
Among such the liquid jet recording methods, those disclosed, for example, in Japanese Laid-open Patent Application No. 51837/1979 and German Laid-open Patent Application (DOLS) No. 2843064 have characteristics different from certain other liquid jet recording methods in that heat energy is caused to act on liquid to thereby obtain a driving force for liquid droplet discharge.
That is, the recording methods disclosed in the above-mentioned publications are characterized in that liquid subjected to the heat energy causes a state change which may result in a sharp increase in volume and, by the force resulting therefrom, liquid is discharged from an orifice at the end of the recording head portion, whereby flying liquid droplets are formed, adhere to the recording medium and thus accomplished recording.
Especially, the liquid jet recording method disclosed in DOLS No. 2843064 is not only very effectively applicable to the so-called drop-on demand recording method, but also readily permits the recording head portion to be of the full line type with a very dense multi-orifice arrangement, so that images of a high degree of resolution and high quality can be obtained at a high speed.
The recording head portion of apparatus applied to the above-described recording method is provided with a liquid discharging portion having an orifice provided to discharge liquid and a liquid flow path communicating with the orifice and having as a part of the construction thereof a heat-acting portion, in which heat energy for discharging liquid droplets acts on the liquid, and an electro-thermal converting element as means for generating heat energy.
This electro-thermal converting element is provided with a pair of electrodes and a heat-generating resistance layer connected to these electrodes and having a heat-generating area (a heat-generating portion) between these electrodes, and generally has in the upper portion thereof a protection layer covering the electrodes and the surface of the heat-generating portion and is formed on an insulative base plate. A fragmentary cross-sectional view for illustrating a typical structure thereof is shown in FIG. 1 of the accompanying drawings.
As shown in FIG. 1, an electro-thermal converting element 101 has a structure in which there is layered, in this order a back-up member 102 formed of silicon, glass or ceramics, a lower layer 103 disposed on the back-up member 102 and formed of SiO.sub.2 or the like, a heat-generating resistive layer 104 for generating heat energy on the lower layer 103, an electrode layer 105 formed of Al or the like, layered on the heat-generating resistive layer 104 and supplying a current corresponding to a signal, a first upper layer 106 formed of SiO.sub.2 or the like and protecting the heat-generating resistive layer 104 and the electrode layer 105, a second upper layer 107 formed of polyimide resin or the like for making up for any defect of the first upper layer 106 and a third upper layer 108 formed of Ta or the like and reinforcing the mechanical strength. Although the upper layers are shown as a three-layer structure, three layers are not always necessary but one to two layers may also be used or four or more layers may sometimes be used for protection. If the heat-generating resistive layer 104 or the electrode layer 105 has an ink-resisting property and has a sufficient mechanical strength, the upper layers need not always be provided.
Now, if the electro-thermal converting element 101 is seen from above with the upper layers removed therefrom, the plan view thereof will be as shown in FIG. 2 of the accompanying drawings wherein a heat-generating portion 109 and a number of electrodes 105-1 and 105-2 for supplying power to cause the heat-generating portion 109 to generate heat are juxtaposed on the lower layer 103.
Formation of the heat-generating portion 109 and the electrodes 105-1 and 105-2 is generally accomplished by the following process. A heat-generating resistive layer 104 consisting of HfB.sub.2 or the like, for example, is formed on the surface of a member comprising the back-up member 102 and the lower layer 103 formed thereon, by a method such as deposition or sputtering, and an electrode layer 105 consisting of Al or the like, for example, is further formed on the upper surface of the heat-generating resistive layer 104 by a similar method. Then, by the use of a photomask having such a pattern as shown in FIG. 3 of the accompanying drawings, a part of the electrode layer 105 and the heat-generating resistive layer is removed by the so-called photoetching method and further, a part of the electrode layer 105 is etched by the use of a photo-mask having such a pattern as shown in FIG. 4 of the accompanying drawings, whereby an electrode and a heat-generating portion of desired shapes are formed at desired positions.
However, it is very difficult to accurately align the pattern shown in FIG. 3 and the pattern shown in FIG. 4 and therefore, after photoetching, such positional deviations as shown in FIG. 5 of the accompanying drawings is liable to occur. As a result, the distribution, density, etc. of the current flowing to the heat-generating portion can become irregular in each manufactured head, and this has caused the durability and reliability of the manufactured recording heads to deteriorate. This in turn has caused irregularity of the resistance value of the heat-generating portion and has lowered the manufacturing yield of the products.